externals 配置项主要用于防止将某些 import 的包（package）打包到 bundle 中，而是在运行时（runtime）再从外部获取这些扩展依赖（external dependencies）。这样做的主要目的是为了解决打包文件过大的问题。
优化前
webpack.config.js
const config = {
entry: './src/index.js',
output: {
filename: 'main.js'
},
mode: 'development',
}
module.exports = config;
src/index.js
import $ from 'jquery'
$(document).ready(() => {
$('body').css({
width: '100%',
height: '100%',
'background-color': 'red'
})
})
优化后
webpack.config.js
const HtmlWebpackPlugin = require('html-webpack-plugin');
const config = {
entry: './src/index.js',
output: {
filename: 'main.js'
},
mode: 'development',
externals: {
$: 'jQuery'
},
plugins: [
new HtmlWebpackPlugin({
template: './index.html',
})
]
}
module.exports = config;
src/index.js
$(document).ready(() => {
$('body').css({
width: '100%',
height: '100%',
'background-color': 'red'
})
})
index.html
<!DOCTYPE html>
<html lang="en">
<body>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.7.1/jquery.min.js"></script>
</body>
</html>
可以看到将jquery排除在打包内，节省了319-177=144ms
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